Electric-wave transmission system



May 28, 1929. G. H. sTx-:vENsoN :1,714,697

ELECTRIC WAVE TRANSMISSION SYSTEM Filed May 2, 1925 Patented May28,1929.

GEORGE H. STEVENSON, OF NEW YORK.

vApplication led May 2,

This invention relates to. electric wave transmission systems and moreparticularly to means for generating and selectively transmittingelectric waves.

An object of the invention is to generate electric waves and toselectively transmit the generated waves to a load device.

Another object is to selectively transmit complex waves and to preventthe production of transient surges in the transmission `path.

An additional object is to compensate for reactance in a path traversedby electric waves to render it substantially non-reactive.A

A further object is to neutralize the ,reactancefof a band transmissionnetwork by another reactive network to produce a nonreactive network ot'constant impedance for all frequencies both within and without thetransmission band. f

An additional objectis to prevent current or voltage surges lof largeamplitudewhen an electric current traversing reactive paths is varied. c

A featulc of the invention is a network s included in an interruptercircuit which has a constant non-reactive impedance for all frequenciesand a broad band filter transmission characteristic.

-Another feature is an interrupter having' its magnet winding includedas an element of a non-reactive network. f A VJfurther feature is ameans for coupling space discharge tubes, which means comprises a broadband filter having jparallel paths, one bearing a complementaryrelationto: the other, whereby the two form a' nonreactive, const-ant impedance"path at all frequencieseither within or without the transmission band.

lVhen an electric currentis interrupted or the impedance of the pathwhich it' traverses is subjected to adrupt changes, waves or surges ofcurrent or voltage or both, of large am litude may be produced if thepath inclu es reactive element-s. A practical illustration of a casewhere such surges are likely to occur and where they are detrimental isin a circuit for generating yvarying current by means of a circuitinterrupter such as has `been employed in telephone systems forgenerating low lfrequency currents for ringing purposes.

e It is now known that waves of rectangular YORK, N. Y., ASSIGNOR, TOWESTERN ELECTRIC COMPANY, INCORPORATED,

I Technical Journal A CORPORATION OF NEW ELECTRIC-WAVE TRANSMISSIONSYSTEM.

1925. serial No. 27,376.

form, such as are produced by interrupting a direct current, contain aninfinite series of components with difierent amplitudes. See an articleby Ralph V. L. Hart-ley entitled ARelations of carrier and sidebands inradio transmission published in the Bell System for April, 1923, page90. Then waves of this form are generated in or transmitted over acircuit including reactive paths, the resonance property of the reactiveelements causes the components of the wave corresponding to the resonantfrequencies to develop currents or voltages of large amplitude which maybe termed surges or transients For example the winding of theinterrupter magnet in a ringing interrupter system of this kind willordinarily provide a resonant path, since it has inductance anddistributed capacity and hence will cause transient surges ofdetrimental character, One disadvantage resulting ence of these surgesin a telephone line, for example, is that inductive interference betweenadjacent lines may be produced. Another disadvantage is that the surgesmay be of a frequency such as to cause undesired operation of Abells orotherkg signals in the system. y

If a filter network of the ordinary kindI be provided to`discriminateb'etween desired and undesired frequencies, the reactancesof the filter elements will likewise provide resonant paths forproducing other transients in the manner explained above.

In the present invention, a broad band filter network is included in acircuit with a variable impedance device and a source of current,representative of any source of complex waves, and a load circuit.,representing any desired form of wave receiving arrangement or device.The filter network, as a whole, comprises two parallel paths orcomplementary filters so designed that their resultant impedancemeasured at the input terminals is a constant resistance frequencies.Each filter has a broad band transmission characteristic and the twocombined have a similar characteristic.

The two paths of the iilter are rendered complementary by providingseries impedances in one corresponding to shunt admittancesin the other,series coils corresponding to shunt condensers, series condens- BY MEsNEASSIGNMENTS,

from the pres-- at all y components of its impedance should be verylarge as compared to its reactive component. This requirement isordinarily met in etlicient signal receiving arrangements.

The invention is illustrated in the drawings wherein:

Fig. 1 represents an interrupter circuit including a filter having anon-reactive impedance;

Fig. 1a represents a modified terminal element for the filter of Fig. 1;and

Fig. 2 represents a wave translating circuit including space dischargetubes coupled by means of a non-reactive band pass filter.

In the several iguies of the drawings like reference characters havebeen used to indicate like parts.

The circuit shown in Fig. 1 comprises a variable impedance device,namely an interrupter 10, including a magnet 11 having an armature 12and a Contact 13. The winding ot magnet 11 is included in a circuit witha battery 14 in series withcontact 13 and armature 12. The winding ofmagnet 11 is shunted by a path including a resistance 15 in series witha capacity 16. The terminals 17 and 18 of the interrupter connect to theinput terminals of av band filter 19 including terminal impedanceelements 20 and 21 preferably resistances.

The band filter 19 includes parallel transmission paths or componentbroad band filters 22 and 23. Path 22 has series inductancc elements 24,shunt inductaiice elements 25, series capacity elements 26 andshunt.ca,`

pacity elements 27. Path 23 contains similar elements 24', 25', 26 and27 The two paths of filter 19 have their output terminals connected to.independent .primary windings of a three-winding transformer 28, thesecondary winding of'which is connected to a resistance in path 30representing any eiicient load circuit or device the impedance of whichis chiefly resistance.

The transformer 28 may be omitted and resistance 30 replaced by theelements shown in Fig. 1a which include separate resistances 31 and 32representing separate load devices or elements arranged to be connectedto the respective output terminals of the vpaths 22 and 23. i l

The winding of magnet 11 is energized by means of current from battery14 whereby its armature is caused to alternately/open and close contact13. Interrupter 10- and battery 14 represent any desired source oflcomplex waves. The current supplied from source 14 to filter 19 is thussubstantially in the form of rectangular waves. It has been explainedthat when a direct current is interrupted or when Waves of rectangularform are supplied to a path including reac tance elements that surges ortransient voltages or currents will ordinarily be produced. In thepresent invention, however, the path Vincluding the elements 15 and 16is provided to compensate for the reactance of the winding of magnet 11to render the wholey path non-reactive. Tn order for the one path tocompensate for the other their respective time constants niust be thesame and their resistances must be equal. Again, the paths 22 and'23 offilter 19 are designed to be of a complementary nature, so far as thereactance of these paths is concerned, so that the i filter, as awhole,visjsubstantially non-reactive at all frequencies. By virtue ofthis fact, when waves of rectangular or other complex form orinterrupted direct current are supplied to the filter 19, transientsurges are prevented from being produced in the input circuit. Moreover,the',J filter functions 'to transmit a desired band of fre-y quenciesfrom the intei'rupter 10 to the loadA and to exclude any undesiredfrequencies which may be present as components of the rectangular wavesproduced by the source. 'In addition, the impedance of filter 19 isconstant for all frequencies.

The resistances 30, 31and 32 may be replaced by any load circuit ordevice, such, for example, as a telephone line including telephoneringers and the like.

In order that path 22 of filter 19 may be the proper counterpart of path23, the series coils 24 in one correspond to shunt condensers 27 in'tlieother and the Series condenseis 26 in one path correspond to bridged orshunt coils 25 in the other path. Y

In the article entitled Theory and design of uniform and compositeelectric wave filters by Otto J. Zobel, published in The Bell SystemTechnical Journal Vol. II,

January, 1923, page 1, it is shown that, 4to

any non-dissipative reactance network there corresponds an inversereactance net-.

Work which is so related that the product 'of their impedance is aconstant, independent vof frequency. The rules byv which vin'versenetworks may be designed are developed under the heading Theorem i2-jonpage 360i theabove journal.

It may further be shown Work of filters 19 of Figf 1 and 19 of Fig. 2,

the product of the corresponding imp edances of the component-networksvis a constant and moreover that the result-ant impedance. isv a pureresistance. A

-Let Zrepresentthe'impedance of either `filter or 19 measured at theIinput ter- RZ1 RZ2 R+Z1+1ie+z2 R when 'Z,Z2=R2. This expression setsforth the relation which impedances Z, and Z2 must bear to each other inorder that the total impedance Z shall be a constant resistance; inother words,in order that the filters 19 or 19', as thecase may be,shall be of non-reactive and constant impedance. If one impedance Zl begiven, the impedance Z2 may bedetermined from these relationships as setfort-h by Zobelin the above mentioned article.

f nowin a practical case one branch of the filter 19, such as branch 22,be designed that filter to be a broad band filter of a particular type,then in accordance withy the present invention an inverse network 23 maybe designed and this inverse network will be a broad band filter havingtransmission characteristics similar to the network 22. l

In the present instance filters 19 and 19 comprise each a filter 22 ofthe constant k type. The distinguishing characteristic of a constant kfilter is that the product of its series and shunt impedances is aconstant real'quantity dimensionally of the type (resistance) 2. Theinverse filter network 23 in each case is also a constant c filter. Itis not to be understood, however, that these filters are necessarily ofthis type for they may be of any general type whether constant A 1 ornot, this particular-type of filter having been used as an illustrationmerely from conlsiderations of convenience.

In order that 'the construction of an inverse filter network may bebetter understood, a practical case will now be illusstrated. For thispurpose, in Fig..2 the various shunt and series elements of thecomponent filters are designated as Zm Z 217 Z12 and Z22, respectively.It is to be noted 22 is terminated in mid-series at 4both ends, whereasflter23 is terminated in mid-shunt at both ends.

Ifit be assumed that the filter 22 is the given impedance Z1, thenapplying the rules laid ddwn by Zobe the reciprocal network 23 may bevconstructed, in whichY series ele-v y ments correspond to 'shuntplementsof the filter 22 and vice versa, and series .combinations of elements 1none correspond to shunt combinations of elements in the other. The

vrelationships which must exist between various impedances are asfollows:

I R1R2=Z11Z22-=Z21Z12=-R2 This equation shows that the propagationconstants-of the component filters are alike,

since by well-known filter theory Cosh P1=1+}% 2l Cosh P2=1 +lg`12 22where P1 and P2 are the respective propagation constants of a singlecomplete section of each filter respectively. A

In Fig. 2, a filter 19 in general similar to the filter 19 shown inF ig.1, is arranged to couple the output circuit of a space dischargerepeater 35 to the input circuit of a second space discharge repeater36. Repeaterl 35 includes aspace discharge tube 37 having a grid cathodeand anode. Input terminals 38 and 39 are connected to the grid andcathode respectively and are shunted by a resistance 40 which provides aleak path for currents between thegrid and cathode.

` A battery 41 of suitable electromotive force is provided to supplytube 37. The output circuit of tube 37, which is connected to its anodeand cathode, includes 'a source of space current represented by battery42 connected in series with a choke coil 43.' The output circuit iscoupled to the filter 19 bymeans of a condenser` 44. The outputterminalsof transformer 28 are connected to the input electrodes of a spacedischargev` tube 45 and include in shunt thereto, the

resistance 30. In series in the input circuit of space discharge tube 45is included a battery 46 for supplying a suitable 4average potential tothe control electrode. The output circuit of this tube also includesaspace current source 47 in series with choke coil 48 and is connected tooutput y and shunted by a high impedance repre= sented by resistance 49.Electric waves of any desired form may be supplied-to the input circuitof tube 37 to produce fluctuations of the potential upon` the controlelectrode thereof and to cause corresponding .fluctuations in thecurrent traversing the space path in the tube. Byproviding batteries 41and 42 having suitab'le voltages, the fluctuations produced inthe outputcircuitof tube 37 may be caused'to be of greater am'- plitude thantheco'rresponding Waves su plied to its inputJ circuit. Filterr19 servesllO terminals 29 to selectively transmit 'the waves suppliedA which maysupply any suitable load circuit,

or device, as already mentioned in connection with Fig. 1. Filter 19 maybe designed to passany desired band of frequencies and to excludefrequencies outsidev of the selected band. Moreover, this filter whichincludes the two paths-22 and 23, similar to corresponding paths offilter 19, is preferably rendered non-reactive by making one paththereof the counterpartof the other. That is, series coils in onecorrespond to bridged condenser-s in the other, andseries impedances inone correspond to bridged impedances in the other.

An important advantage of the filter 19 as a coupling between the spacedischarge tubes 37 and 45 is that, being substantially non-reactive, thetendency for the amplifiers to establish parasitic oscillations orsinging in the system is greatly reduced. y

It is to beunderstood that the invention herein described .is capable"of gene-ral application and is not to be limited to the claims.

specific embodiments disclosed but only-as indicated by the scope Whatis claimed is: v Y Y 1. In a wave transmitting system, a wave source, aload circuit, and a filter network connected'between said source andsaid circuit, said filter network comprising two sep- 1arate filters fortransmitting ,waves mdepepdentlybetween said source and said c1rcuit,said separate filters being complemenv tary' asg'regards theirreactance'.

2. In a wave transmittingsystem a source `of complex waves, a wavetfilter connected thereto and including .reactive impedance elements,and a load circuit connected to the output terminals of said wavefilter, said filter comprising two portions included in separate wavechannels, said portions being complementary with respect to theirimpedances and including resistance elements of the appended whereby theimpedance of the system to waves from said source is made a constantresistance at all frequencies.

3. In an nterrupter circuit, a source of waves, including aninterrupter, a load circuit., a plurality of filters arranged totransmit in parallel between said source and said load circuit, saidfilters being complementary, whereby their combined impedance to wavesof all frequencies is substantially,

constant and non-reactive.

4. In4 an electric wave vtransmission sy:-

tem, a source of waves, a load device, a resistance connected to saidsource, and a filter terminated by said resistance, said filtercomprising a plurality of component filter networks, each terminated byindependent portions of said resistance, said filter as a whole beingsubstantially non-reactive. 5. An electric wave transmission system inaccordance with claim 4, characterized in this that said independentportions of said resistance are equal.

6. ln an electric wave transmission system, a. source of waves, a loaddevice, a resistance in two equal parts R, and R2 connected to` saidsource anda broad band filter ferminated by said resistance, saidlfilter comprising two component filter networks terminated respectivelyin the parts R, and R2 of said resistance, the first component filterhaving series elements' of impedance Z1l and shunt element-s ofimpedance Z2, and the `other component filter having series impedanceelements Z1, and shunt impedance elements Z22 said lters beingsodesigned that 7. 'A wave transmission networkscompris- GEORGE H.STEVENSON.

